Agriculture Reference
In-Depth Information
the results being highly species specific. Elevated
ambient CO
2
concentrations had no effect on
B. tabaci
, but affected
T. vaporiarum
negatively.
Elevated CO
2
had little effect on populations of
the important thrips tospovirus vector species,
Frankliniella occidentalis
, but might increase
population sizes of some other thrips vector spe-
cies (Jones and Barbetti, 2012).
different strains induced in potato plants or virus
indicator hosts were used to distinguish strain
groups (i.e. pathotypes) or strains. For example,
the reactions of potato cultivars differing in sin-
gle gene hypersensitive resistances (differentials)
were used to distinguish the different strain
groups of PVX, PVY, and PVA (Cockerham, 1955;
Jones, 1982b, 1990; Valkonen
et al
., 1995).
With PVY, the ability to induce necrotic symp-
toms in tobacco was also used in addition to
potato resistance genes. With PVS, systemic in-
vasion of the indicator host,
Chenopodium
quinoa
was used to distinguish Andean from ordinary
strains (Hinostroza-Orihuela, 1973; Santillan,
1979; Santillan
et al
., 1980). With PLRV, strains
were defined by the severity of the symptoms
they induced in potato plants or the diagnostic
indicator host,
Physalis floridana,
, mild strains
sometimes causing latent infections (Wright
et al
.,
1967; Chiko and Guthrie, 1969). Serological
differences or specific monoclonal antibodies
(MAbs) were also used to distinguish strains of
some potato viruses. For example, MAbs were
used to distinguish strains of common potato
viruses, such as PVY (Ellis
et al
., 1977), or APLV
and APMoV in the Andean region (Fribourg
et al
.,
1977a,b; Koenig
et al
., 1979). When viral nu-
cleic acid sequencing and phylogenetic analysis
became widely available, grouping of nucleotide
sequences provided another avenue to distin-
guish potato virus strains. A problem then arose
due to attempts to use biologically derived potato
virus strain nomenclature for phylogenetically
distinguished strains without knowledge of
whether the two systems actually coincided or
which viral genes influenced symptom formation.
The paragraphs that follow discuss examples
and solutions to the nomenclature confusion
that has resulted.
Implications for seed potato production
Rising temperatures in formerly cooler regions
are likely to have serious implications for potato
seed production. This is not only because of in-
creased aphid vector activity but also because of
factors like greater survival of volunteer pota-
toes arising from milder winters, or the intro-
duction of other Solanaceous crops that act as
infection reservoirs for aphids or potato viruses
but require warmer summer growing conditions
than were available formerly (e.g. tomato, pep-
per). Seed production areas in some parts of the
world are likely to become unsuitable for high-
quality seed tuber production, necessitating
moves away from formerly cooler regions, such
as ones at lower altitude or in windswept coastal
areas, to higher-latitude regions formerly too
cool for growing potatoes, or to cooler, higher
altitudes in highland regions.
Epidemiological modeling approaches have
been adopted to predict PVY spread in potato
crops in northern Europe (Sigvald, 1986; Dor-
ing, 2011; Kirchner
et al
., 2011). More such
models are needed with other common potato
viruses and in other regions (Jones
et al
., 2010).
Moreover, modeling studies are lacking on the
possible effects of different climate change scen-
arios on the spread of common potato viruses
and their worldwide geographical distributions
(e.g. Jones and Barbetti, 2012).
Potato virus S
strains
With PVS, when the biologically defined Andean
strain (PVS
A
) was found outside the Andean re-
gion (e.g. in Europe, North America, and New
Zealand) and the coat protein (CP) genes of three
European isolates were sequenced, these grouped
with ordinary strain PVS isolates (PVS
O
). By
contrast, when the CPs of three other PVS iso-
lates defined as Andean biologically (from Peru, India,
and an unspecified country) were sequenced,
12.3 Rationalizing Biological and
Phylogenetic Potato Virus
Strain Nomenclature
Before the advent of large-scale nucleic acid se-
quencing technologies, strains of common potato
viruses were defined biologically or serologically.
Distinct differences between the symptoms that
